Multi-level linear modulation schemes such as M-ary Quadrature Amplitude Modulation (QAM) are commonly used in today's microwave radio systems to provide spectrally efficient radio communications for mobile backhaul and other applications. Due to the non-constant envelope of these modulation schemes, they are more sensitive to the power amplifier non-linearity. Among many linearization techniques, predistortion is a commonly used technique that involves the insertion of a non-linear element prior to the power amplifier such that the combined transfer function is a linear one. For example, the open-loop digital predistortion (DPD) models the non-linearity of the power amplifier as an odd-order polynomial, each predistortion polynomial coefficient being a complex number represented by a pair of real and imaginary components. Since the performance of a power amplifier varies with its operating conditions, e.g., frequency, channel bandwidth, temperature, etc., the predistortion coefficients to be applied to the power amplifier should be updated accordingly to keep track of the changes in the operating conditions.